Astrolabe (Greek, astrolabon, "star-taker"). A historical astronomical instrument used by astronomers, navigators, and astrologers. Its many uses include locating and predicting the positions of the sun, moon, planets, and stars; determining local time given local latitude and vice-versa; surveying; triangulation; and casting horoscopes

Axis. An imaginary line around which an object rotates. In a rotating sphere, such as the earth and other planets, the two ends of the axis are called poles. The23.45 degrees tilt of the earth's axis with respect to the plan of its orbit around the sun causes the Northern and Southern Hemispheres to point toward and away from the sun at different times of the year, creating seasonal patterns of weather and climate.

Constellation. Any of various groups of fixed stars to which definite names have been given, such as Ursa Major, Ursa Minor, Bootes, Cancer, Orion; a division of the heavens occupied by such a group.

Decan. Any of three divisions of 10 degrees within a sign of the zodiac; a subdivision of a major sign.
The word means "a part", and is used of the three parts into which each sign is divided, each of which is occupied by a constellation.

Ecliptic. The intersection plane of the earth's orbit with the celestial sphere, along with the sun appears to move as viewed from the earth.

Ecliptic Path. The path marked by the sun as the earth revolves around it during a one year period.

Equinox. Either of two points on the celestial sphere at which the ecliptic intersects the celestial equator. (Note: This makes for two equal-length days and nights on the earth, one of which occurs in the spring and one in the fall of each year.)

Planisphere. Astronomy. A polar projection of half or more of the celestial sphere on a chart equipped with an adjustable overlay to show the stars visible at a particular time and place

Precession of the equinox. A slow westward shift of the equinoxes along the plane of the ecliptic, resulting from precession of Earth's axis of rotation, and causing the equinoxes to occur earlier each sidereal year. The precession of the equinoxes occurs at a rate of 50.27 seconds of arc a year; a complete precession requires 25 ,800 years.

Supernova. A rare celestial phenomenon involving the explosion of most of the material in a star, resulting in an extremely bright, short-lived object that emits vast amounts of energy.

Zodiac. a. Astronomy. A band of the celestial sphere extending about 8 degrees to either side of the ecliptic that represents the path of the principle planets, the moon, and the sun. b. In astrology, this band divided into 12 equal parts called signs, each 30 degrees wide, bearing the name of a constellation for which it was orgininally named but with which it no longer coincides owing to the precession of the equinoxes.